Nick Clegg and David Cameron have been urged to pass legislation on the green investment bank. Photograph: Wpa Pool/Getty Images

Green businesses, investors and campaigners have made a last-ditch plea to the government over its green investment bank, urging ministers to give key assurances to ensure cash will flow into the UK's low-carbon economy.

Details of the bank – the government's flagship environmental policy, intended to spark tens of billions of investment to transform the UK's infrastructure – will be set out by Nick Clegg at 12.30pm today in the City. But rows among ministers anxious to keep control of the new bank mean its powers are likely to be curtailed.

One key question is over whether the bank's rules should be enshrined in legislation, rather than left to the whim of ministers. Another is whether the bank will have borrowing powers in future, with the Treasury expected to try to disappoint investors and water down guarantees on borrowing. One of the options Treasury mandarins are pushing is that the bank should only be allowed to borrow money from the government, rather than from the private sector – an amendment that investors say would make a nonsense of the institution.

Penny Shepherd, the chief executive of the UK sustainable investment and finance association, representing investors, wrote to David Cameron and Nick Clegg to call for legislation on governance of the bank, and to ensure that it will have powers to borrow money, independent of government.

She said: "Following the financial crisis, Sir David Walker recommended stronger and more effective governance of banks and other major financial institutions to protect the public interest. Good governance and transparency are as essential for the success of the green investment bank as any other banking institution."

The green investment bank is to be formed using up to £3bn of capital from government, which will be invested in low-carbon projects that would otherwise be hard to finance, such as infrastructure improvements, offshore wind farms and marine energy.

But after months of wrangling among ministers, some of the key powers of the bank have been reduced. It will not be allowed to borrow money for several years after it is set up, and it will not be allowed to issue green investment products, such as green ISAs and green bonds. These changes to the original proposals for the bank have dismayed green investors and campaigners.

Green businesses are also anxious over the extent to which ministers will be able to control the bank in future. They want the bank to have a greater degree of independence from ministers, to minimise the risk of political interference in its investment decisions.

Andrew Raingold, the executive director of the Aldersgate Group, which represents environmental businesses, said: "The cabinet row over carbon targets last week demonstrated the uncertainty over long-term green commitments. Businesses must be sure that policymakers will stick to their guns if we are going to see a step-change in investment for clean technologies."

He added: "A green investment bank that is enshrined in legislation will provide the strongest possible signal that the institution is permanent and will be at the heart of the government's plans for a green industrial revolution."

Ed Matthew, the director of Transform UK, a green campaigning organisation, also urged the government to resist attempts by some in Whitehall to delay the setting up of the bank, in order to ensure greater control over it. "The government must announce they will set up the green investment bank in legislation next year and confirm that the bank will have the power to borrow from the capital markets. These are critical features that will ensure the bank is enduring, has operational independence and the power to leverage in high levels of private capital into the low carbon economy," he said.

"But no doubt the Treasury trolls will do everything they can to sabotage these borrowing powers. By continuing to undermine one of the most important solutions for tackling climate change and building economic resilience, they are posing a clear and present danger to this country's national security."